Preparation method of ZnO@ZnS nanocomposite with strong ultraviolet emission characteristics

Abstract

This invention discloses a method for preparing a ZnO@ZnS core-shell structured nanocomposite material with strong ultraviolet emission properties. To minimize visible light interference and enhance the ultraviolet exciton emission of ZnO, ZnS is used to modify the ZnO surface to construct a core-shell structured composite material. This effectively passivates ZnO surface defect states and suppresses / isolates surface adsorbates. Simultaneously, the wider band gap of the ZnS shell localizes ZnO excitons, preventing them from diffusing to non-radiative recombination centers, thereby improving exciton radiative recombination efficiency and significantly enhancing ultraviolet exciton luminescence intensity. The ZnO@ZnS core-shell structured nanocomposite material prepared by this invention exhibits good crystallinity and strong ultraviolet luminescence properties, making it suitable for high-performance ultraviolet optoelectronic devices. This invention has advantages such as simple preparation process, good stability, short cycle time, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to a method for preparing ZnO@ZnS core-shell structured nanocomposites with strong ultraviolet emission properties. This method prepares ZnO@ZnS core-shell structured nanocomposites with strong ultraviolet emission properties through surface sulfidation, which belongs to the field of optoelectronic functional materials. Background Technology

[0002] Photodetectors (PDs) convert light signals into electronic signals and are widely used in biomedical imaging, environmental monitoring, optical communication, and defense industries. Commonly used semiconductor ultraviolet (UV) photodetectors are made from wide-bandgap semiconductors such as GaN, SiC, Ga₂O₃, ZnO, and diamond. Among these, ZnO plays a crucial role in detecting and analyzing UV light due to its excellent environmental friendliness and biocompatibility. However, in addition to the typical UV emission originating from near-band edge exciton recombination, ZnO exhibits broadband emission in the visible light region related to transitions to intrinsic defect states at deep energy levels. This visible light emission significantly affects the UV emission intensity of ZnO and its applications. Therefore, to achieve controllable UV emission applications using ZnO, selective emission modulation and optimization are necessary. Coating its surface with organic polymers or inorganic layers (amorphous, semi-crystalline, or crystalline), or constructing heterojunction composite materials, can effectively modulate and optimize the UV emission performance of ZnO.

[0003] Inorganic materials such as SiO2, MgO, and ZnS, as well as metals (such as Zr, Hf, or Zn), are commonly used coating materials. Among them, ZnS is a non-toxic semiconductor with a wide bandgap (3.72 eV) and similar physical properties to ZnO. Furthermore, ZnS and ZnO have good compatibility, making it suitable for modifying ZnO to construct composite materials. Li et al. reported enhanced ultraviolet exciton luminescence in ZnS-coated ZnO nanowires. Wu et al. also recorded the effect of ZnS coating on the ultraviolet exciton luminescence of ZnO nanorods. Ali et al. observed enhanced ultraviolet exciton luminescence in ZnO by passivating ZnO nanorods with ZnS. Li et al. combined nitrogen annealing with ZnS layer deposition and found that the intensity of ZnO ultraviolet exciton luminescence increased by approximately 2.5 times at room temperature. Fang et al. increased the ultraviolet exciton emission intensity of ZnO nanowires by 4 times through ZnS coating.

[0004] To this end, this invention develops a method for preparing ZnO@ZnS core-shell structured nanocomposites with strong ultraviolet emission properties. The method involves first synthesizing well-crystalline ZnO nanoparticles with an average particle size of approximately 100 nm using a hydrothermal method; then, thioacetamide (C2H5NS) is used to form a dense ZnS shell on the surface of the ZnO nanoparticles via surface sulfidation, resulting in a controllable ZnO@ZnS core-shell structured nanocomposite with 10 times stronger ultraviolet emission compared to ZnO nanoparticles. Summary of the Invention

[0005] This invention provides a method for preparing ZnO@ZnS core-shell structured nanocomposites with strong ultraviolet emission properties. The method involves first using zinc salt (Zn(NO3)2·6H2O) as the zinc raw material, citrate (K3C6H5O7) as the complexing agent, and alkali salt (KOH) as the precipitant, followed by a hydrothermal reaction at 100–180 °C for 1–10 h to obtain ZnO nanoparticles. Subsequently, thioacetamide (C2H5NS) is selected as the sulfur source, and a hydrothermal reaction at 50–150 °C for 12 h is performed to obtain the ZnO@ZnS core-shell structured nanocomposites.

[0006] This invention demonstrates significant technical advantages. Well-crystallized ZnO nanoparticles are obtained via a hydrothermal method, followed by ultrasonic dispersion and a sulfidation reaction with thioacetamide (C2H5NS). During the hydrothermal reaction, C2H5NS undergoes hydrolysis, releasing H2S into the aqueous solution (Equations (1-2)). This H2S readily reacts with ZnO at the interface of the ZnO nanoparticles, promoting the formation of ZnS crystal nuclei. Since ZnO in the solution... 2+ and S 2- Concentration gradient of ions, Zn 2+ Ions will diffuse outward into the shell, while S 2- Ions diffuse inward to the core layer, as shown in equation (3). As the reaction progresses, when the ZnS nucleus size reaches a certain level, H2S becomes extremely difficult to diffuse to the fresh surface of the ZnO nanostructure and react with ZnO. Furthermore, due to the limited sulfur source, reaction (3) will terminate. Ultimately, a uniform and dense ZnS shell is formed. The relevant chemical reactions can be represented as: CH3CSNH2 + H2O→ CH3(NH2)C(OH) + SH (1) CH3(NH2)C(OH)SH + H2O→ CH3(NH2)C(OH)2 + H2S (2) H₂S + ZnO → ZnS + H₂O (3) Therefore, the advantages of this invention are twofold: First, by modifying the surface of ZnO nanoparticles with a ZnS shell, a core-shell structured nanocomposite material is constructed, which effectively passivates the defect states on the ZnO surface and inhibits / isolates surface adsorbates. At the same time, the wider band gap of the ZnS shell can localize ZnO excitons, preventing them from diffusing to non-radiative recombination centers, thereby achieving strong ultraviolet luminescence performance. Second, the preparation process of this invention is simple, has good stability, short cycle time, and high yield, which can save production costs to a certain extent. Attached Figure Description

[0007] Figure 1 This is the XRD pattern of the ZnO@ZnS core-shell structured nanocomposite material prepared in this invention.

[0008] Figure 2 This is a transmission electron microscope (TEM) image of the ZnO@ZnS core-shell structured nanocomposite material prepared in this invention.

[0009] Figure 3 This is the photoluminescence emission spectrum of the ZnO@ZnS core-shell structured nanocomposite material prepared in this invention under 365 nm ultraviolet light excitation. Detailed Implementation

[0010] The method for preparing high ultraviolet-emitting ZnO@ZnS core-shell structured nanocomposites of the present invention is described in detail below: Zn(NO3)2·6H2O, K3C6H5O7, and KOH were used as raw materials, with K3C6H5O7 acting as a complexing agent and NaOH as a pH adjuster. The precursor solution had a Zn²⁺ concentration of 0.1 mol / L, and the concentration of the complexing agent K3C6H5O7 was Zn²⁺:(C6H5O7). 3- The molar ratio is 10:2; the concentration of the pH adjuster NaOH is prepared to be 0.5 g / ml to 1 g / ml.

[0011] (2) To prepare a 0.1 mol / L precursor, weigh the corresponding amounts of Zn(NO3)2·6H2O and K3C6H5O7 using a precision electronic balance. Put the weighed raw materials into a 100 ml glass beaker, add an 85% ethanol solution, and ultrasonically stir for 30 min to dissolve the raw materials evenly. (3) Add NaOH, a pH adjuster, dropwise slowly to the solution obtained in (2), and monitor the pH value of the solution in real time to control the final pH to 7; (4) Continue stirring the solution obtained in (3) for 60 min to obtain a homogeneous system. Then transfer the mixture to a high-pressure reactor lined with polytetrafluoroethylene and keep it at 180 °C for 12 h. Allow it to cool naturally to room temperature. (5) Centrifuge the reaction mixture obtained in (4), remove the supernatant, wash the precipitate three times with deionized water (the deionized water was heated to 60 °C in advance), and then wash it three times with anhydrous ethanol. (6) After centrifugation, the solid is placed in a constant temperature drying oven and dried for 12 hours, then the product is collected. The temperature of the constant temperature drying oven is 60 °C. (7) Weigh the obtained ZnO nanoparticles according to the stoichiometric ratio and add them to 20 ml of deionized water for ultrasonic dispersion for 20 min; (8) Zn 2+ :S 2- Weigh C2H5NS at a molar ratio of 10:4 and add it to the (7) mixed solution, and continue stirring and mixing for 30 min; (9) Transfer the mixed solution obtained in (8) into a high-pressure reactor lined with polytetrafluoroethylene, keep it at 100 °C for 12 h, and let it cool naturally to room temperature; (10) Centrifuge the reaction mixture obtained in (9), remove the supernatant, wash the precipitate three times with deionized water, and then wash it three times with anhydrous ethanol. (11) After centrifugation, the solid was placed in a 60 ℃ constant temperature drying oven and dried for 12 h before the product was collected.

[0012] Figure 1 X-ray diffraction (XRD) patterns of the prepared ZnO@ZnS core-shell nanocomposites are shown, where the horizontal axis represents the diffraction angle (2θ) in degrees (º) and the vertical axis represents the diffraction intensity. The XRD patterns show reflections from the (100), (002), (101), (102), (110), (103), and (112) planes, confirming that all samples are polycrystalline and possess a hexagonal wurtzite crystal structure of ZnO with space group P63mc (JCPDS 36-1451). Furthermore, a new diffraction peak at 2θ of 28.975º appears, which is a reflection from the (111) plane of ZnS, indicating the formation of the ZnS shell.

[0013] Figure 2 The image shows a transmission electron microscope (TEM) image of the prepared ZnO@ZnS core-shell nanocomposite. The TEM image reveals the microstructure of the obtained ZnO@ZnS core-shell nanocomposite, showing a shell and core with significant differences in color depth. The core corresponds to ZnO, and the shell corresponds to ZnS.

[0014] Figure 3 The photoluminescence emission spectrum of the prepared ZnO@ZnS core-shell nanocomposite material under 365 nm ultraviolet light excitation is shown. It exhibits strong ultraviolet emission under ultraviolet excitation, with an intensity 10 times higher than that of ZnO nanoparticles.

Claims

1. This invention relates to a method for preparing ZnO@ZnS core-shell structured nanocomposites with strong ultraviolet emission properties. First, zinc salt (Zn(NO3)2·6H2O) is selected as the zinc raw material, citrate (K3C6H5O7) is used as the complexing agent, and alkali salt (KOH) is used as the precipitant. ZnO nanoparticles are obtained by hydrothermal reaction at 100~180 ℃ for 1~10 h. Then, thioacetamide (C2H5NS) is selected as the sulfur source, and the reaction is carried out in a water bath at 50~150 ℃ for 6~18 h to obtain ZnO@ZnS core-shell structured nanocomposites.

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